1. Field of the Invention
The present invention relates to a display device, a method of manufacturing such a display device, and an electronic apparatus for use in a portable terminal such as a cellular phone, a PDA (Personal Digital Assistant), or the like which is required to be of a low profile.
2. Description of the Related Art
One of the most important concerns for designing portable terminals is to make themselves low in profile. If a liquid crystal display device for use in a portable terminal display is thick, then it presents an obstacle to efforts to make the portable terminal low in profile. Therefore, there are growing demands for low-profile liquid crystal display devices.
FIGS. 18A and 18B of the accompanying drawings schematically show a cross-sectional structure of a general liquid crystal display device. FIG. 18A shows an overall cross-sectional structure of a liquid crystal panel 100, and FIG. 18B shows the cross-sectional structure in greater detail.
As shown in FIGS. 18A and 18B, the liquid crystal panel 100 includes a transparent insulating substrate (hereinafter referred to as “TFT (Thin Film Transistor) glass substrate”) 101 supporting thereon pixel switches and a driver circuit therefor which are constructed of TFTs, a transparent insulating substrate (hereinafter referred to as “facing glass substrate”) 102 disposed in facing relation to the TFT glass substrate 101, and a liquid crystal display (LCD) layer 106 held between the TFT glass substrate 101 and the facing glass substrate 102 and sealed by a seal member 105.
In an attempt to make the liquid crystal panel 100 low in profile, a semiconductor chip 107 including a control circuit for controlling the driver circuit is mounted as a COG (Chip On Glass) component on the TFT glass substrate 101. The semiconductor chip 107 will hereinafter be referred to as “COG chip 107”.
The use of the COG chip 107 allows design efforts to be made to reduce the total thickness of the facing glass substrate 102, the TFT glass substrate 101, the seal member 105, and polarizing plate and phase difference plate combinations 103, 104 mounted respectively on the facing glass substrate 102 and the TFT glass substrate 101 and also to make the COG 107 thin.
The thickness T1 (e.g., 390 μm) of the COG chip 107 has been designed to be greater than the total thickness T2 (195 μm+80 μm=275 μm) of the polarizing plate and phase difference plate combination 104, the facing glass substrate 102, and the seal member 105 (T1>T2). In FIG. 18A, the liquid crystal panel 100 has an overall thickness T0.
Many proposals have been made to reduce the thickness of liquid crystal display devices.
For example, a liquid crystal display device has a liquid crystal display panel whose opposite surfaces are polished to make itself thin, so that a plurality of liquid crystal display panels can be stacked together for displaying images (see Japanese Patent No. 3290379, paragraphs [0007] through [0013], FIG. 1, referred to as Patent Document 1). After a liquid crystal display panel has been polished into a low profile, a COG chip is connected thereto (see Japanese Patent Laid-open No. Hei 11-104954, paragraphs [0007] through [0009], FIG. 3, referred to as Patent Document 2). The thickness of a COG chip is smaller than the total thickness of a facing glass substrate and a seal member which seals an LCD layer (see Japanese Patent Laid-open No. 2001-350421, paragraphs [0007] through [0008], FIG. 7, referred to as Patent Document 3). Polarizing plate and phase difference plate combinations are in the form of polymer films mounted on a facing glass substrate and a TFT glass substrate by an adhesive (see Japanese Patent Laid-open No. 2003-121641, paragraphs [0006] through [0007], referred to as Patent Document 4). In order to increase the mechanical strength of a glass substrate in a mounting area for a TCP (Tape Carrier Package), the thickness of the glass substrate in a display area is reduced, and the thickness of the glass substrate in the TCP mounting area is increased (see Japanese Patent Laid-open No. 2003-241171, paragraphs [0007] through [0009], FIG. 1, referred to as Patent Document 5).
According to Patent Document 1, however, since a TCP is used as an external terminal, no consideration for the mounting of a COG chip has been made. If a COG chip is mounted on a TFT glass substrate, then the height of the COG chip is greater than the thickness of a facing glass substrate, making it difficult to reduce the thickness of the liquid crystal panel.
According to Patent Document 2, the height of the COG chip may not be made equal to or smaller than the height of a facing glass substrate. The disclosed liquid crystal panel is not suitable for making a liquid crystal display device compact.
As shown in FIGS. 18A and 18B, the liquid crystal panel 100 is fitted with a metal frame 200 serving as a protector for protecting the liquid crystal panel 100 and as a light shield for preventing light from leaking around the liquid crystal panel 100.
The metal frame 200 is vertically spaced from the liquid crystal panel 100 by a space T6. The reasons for the space T6 are that if the metal frame 200 contacts the liquid crystal panel 100, then the TFT glass substrate 101 and the facing glass substrate 102 are deformed, producing cell gap nonuniformities or irregularities in display area, and if the metal frame 200 contacts the COG chip 107, then the COG chip 107 presses the TFT glass substrate 101, tending to increase the contact resistance of the pad for the COG chip 107 or peel off the pad for the COG chip 107.
If the TFT glass substrate 101 and the facing glass substrate 102 cannot ignore the thickness of the COG chip 107, then the thickness of the space T6 is determined by the thickness of the COG chip 107 which includes the driver circuit outside of the display area, rather than by being limited by the device (pixel switch) structure in the display area.
According to Patent Document 3, the liquid crystal panel is made low in profile by making the thickness of the COG chip smaller than the total thickness of the facing glass substrate and the seal member which seals the LCD layer.
Actually, however, the liquid crystal panel includes polarizing plate and phase difference plate combinations, and Patent Document 3 fails to show that the thickness of the COG chip is smaller than the total thickness including the thickness of the polarizing plate and phase difference plate combinations. Depending on the thickness of the polarizing plate and phase difference plate combinations, the metal frame which mechanically protects the peripheral edges of the liquid crystal panel may possibly contact the COG chip. To avoid possible contact between the metal frame and the COG chip, an extra space needs to be provided between the liquid crystal panel and the metal frame.
According to Patent Document 4, polarizing plate and phase difference plate combinations are simultaneously formed of polyester films to produce a low-profile liquid crystal panel. However, the thickness of the films may not be reduced to a minimum because the adhesive and the films need to have a certain level of mechanical strength. Therefore, the proposal according to Patent Document 4 is not effective to manufacture desired low-profile liquid crystal panels.
According to Patent Document 5, the polishing process is complex and involves an increased number of steps. In addition, the area surrounding the pad area needs to be thicker than the TFT glass substrate and the facing glass substrate.
As a result, though the structure proposed in Patent Document 5 is applicable to large-size liquid crystal displays as large as at least 6 inches, it may not be incorporated in smaller liquid crystal display modules because small-size, high-definition liquid crystal display devices as large as at most 6 inches require a polished area other than the pad area.